This invention relates to a hydraulic motor drive system for a decanting centrifuge.
Decanting centrifuges, also called decanters in short, have been used for many years to separate large quantities of mixtures from solids and liquids in a continuous operation. Generally an electric motor which drives a drum by means of belts is used as the drive motor, and a worm which requires low relative speeds but high torques is driven by a torque converter via a co-rotational mechanical drive, with the low-torque connection of the drive being braced against an idle system. Such drive systems have the drawback of exhibiting fixed drive speeds, a feature that often significantly reduces both reliability, efficiency and also the results from a separating point of view.
The infinite variability of the relative speed of the worm is significant improvement. To this end, one category of such drives uses mechanically co-rotational drive units at whose low-torque connection a positive or negative slip is generated, whose degree in a given region can be adjusted arbitrarily.
Another category of such drives foregoes the mechanical drive unit as a torque converter by using a co-rotational, low-speed, high-torque hydraulic motor, whose rotor drives the worm and whose housing is connected to the drum, with the energization being transferred from a pump station, whose quantity can be adjusted, via a high pressure rotary transmission to the rotating system.
Such drive systems allow the relative speed of the worm to be completely independent of the speed of the main drive and, if the rotary transmission has a radial introduction, a coaxial arrangement of the two drive motors is allowed, as taught in U.S. Pat. No. 4,120,447 or French patent No. 2,237,682. Such an arrangement allows belt drives to be dispensed with, especially if the main drive motor has a constant speed. In both drive systems the main drive motor is attached permanently to the machine bed. In addition to the direct and indirect cost savings, this results in the important elimination of transverse forces on the bearings due to the belt tension on the machine main bearing, a state that has a positive effect on the service life and reliability of these highly stressed elements.
Coaxial arrangements, as explained above, require exact centering and alignment of the main drive motor, with an absolutely rigid construction, which incurs additional cost. Such a construction is made even more difficult when the machine rotor has a certain degree of freedom with respect to the idle system, be it for vibrational reasons a radial-elastic bearing suspension or a degree of freedom on an axis arranged at an angle for vertical machines suspended to oscillate. In this case the only way to produce a connection to the main drive motor is with expensive and space-consuming cardan joint systems.